The present application relates to a series of polyamide oligomers based on xcfx89-amino (oligoethyleneglycol) alkanoic acid monomers. These compounds can be used as heterobifunctional crosslinkers which can be conjugated to a variety of biomaterials which include, inter alia, proteins, nucleic acids and lipids. Oligomer-lipid conjugates of this invention can be incorporated into liposomes, micelles and other drug delivery systems for a variety of purposes.
The pharmacokinetics of liposomal formulations can be improved if the vesicles can be maintained in circulation. An important mechanism for clearance of liposomal formulations is thought to involve the adsorption of proteins onto the liposome surface which mediates subsequent clearance by the cells of the reticuloendothelial system (RES). This clearance may be reduced by the attachment of hydrophilic polymers, such as polyethyleneglycol (PEG), to the liposome surface. These polymers may act in one or both of two ways: (i) they may inhibit or stop protein adsorption on to the liposome""s surface, or (ii) they may act as a xe2x80x9csteric barrierxe2x80x9d to inhibit interactions between the cells involved in clearance and any proteins that might be bound to the liposome surface. The steric barrier effect may also be used to inhibit aggregation in some systems.
PEG-lipid conjugates are used in some commercial liposome formulations to create a steric barrier at the liposome surfaces. PEG is attractive because it is cheap, readily available, non immunogenic and is soluble in all but the most apolar of solvents (see, Torchlin, et al., Biochim. Biophys. Acta., 1195:11-20 (1994); Parr, et al., Biochim. Biophys. Acta., 1195:11-20 (1994); and Woodle, et al., Bioconjugate Chem., 5:493 (1994)). The latter properties allow easy conjugation to a wide range of substrates.
U.S. Pat. No. 5,013,556 and European Patent Applications Nos. 0572 049 A2 and 0 354 855 describe liposomes bearing PEG moieties covalently linked to the external surface. As described therein, the PEG moieties are linked to amino groups in the head group of at least one phospholipid species forming the liposomes.
U.S. Pat. No. 4,426,330 describes phospholipids wherein the polar head group has been modified by covalent attachment of a PEG moiety. European Patent Application No. 0 220 797 A2 describes a process for the preparation of liposomes.
One major drawback of the use of polyethylene glycol is that it exists as a distribution of oligomers with different molecular weights. Further, batch to batch variation can occur. Thus, the properties of the PEG-bound liposomes will vary. What is needed in the art is a specific molecular weight material of defined length to allow selective properties to be imparted to liposomes or other drug delivery systems. The present invention fulfills this and other needs.
In one aspect, the present invention relates to an intrinsically heterobifunctional polyamide oligomer (PAO) of Formula I: 
In Formula I, R is a functional group including, but not limited to, hydrogen, alkyl or acyl. R1 is a functional group including, but not limited to, hydrogen or alkyl. In an alternative embodiment, R, R1 and the nitrogen to which they are bound form an azido moiety. R2, in Formula I, is a functional group including, but not limited to, hydrogen, optionally substituted alkyl, optionally substituted aryl or the side chain of any natural or synthetic amino acid or amino acid mimetic. R3, in Formula I, is a functional group including, but not limited to, halogen, hydroxy, alkoxy, mercapto, hydrazino, amino or NR4R5, wherein R4 and R5 are independently hydrogen or alkyl. In Formula I, the index xe2x80x9cnxe2x80x9d is an integer having a value ranging from 4 to 80; the index xe2x80x9cmxe2x80x9d is an integer having a value ranging from 2 to 6; the index xe2x80x9cpxe2x80x9d is an integer having a value ranging from 1 to 4; and the index xe2x80x9cqxe2x80x9d is an integer having a value of 0 or 1.
The parentheses between R and R3 define a monomeric unit. There are xe2x80x9cnxe2x80x9d monomers in any given compound of Formula I. The values of m, p and q and the definitions of R1 and R2 may vary from monomer to monomer for any given value of xe2x80x9cnxe2x80x9d monomers.
In another aspect, this invention relates to a compound of Formula II: 
In Formula II, R1 is a functional group including, but not limited to, hydrogen or alkyl. A, in Formula II, is a functional group including, but not limited to, hydrogen, alkyl, acyl or a ligand. In an alternative embodiment, R1, A, and the nitrogen to which they are bound form an azido moiety. B, in Formula II, is a functional group including, but not limited to, halogen, hydroxy, alkoxy, amino, NR4R5 (wherein R4 and R5 are independently hydrogen or alkyl), mercapto, hydrazino, diacylglycerolyl, dialkylglycerolyl, N,N-dialkylamino, 1,2-diacyloxy-3-aminopropane, 1,2-dialkyloxy-3-aminopropane and a ligand. In Formula II, the index xe2x80x9cnxe2x80x9d is an integer having a value ranging from 4 to 80; the index xe2x80x9cmxe2x80x9d is an integer having a value ranging from 2 to 6; the index xe2x80x9cpxe2x80x9d is an integer having a value ranging from 1 to 4; and the index xe2x80x9cqxe2x80x9d is an integer having a value of 0 or 1. As described above, the parentheses between R and R3 define a monomeric unit. There are xe2x80x9cnxe2x80x9d monomers in any given compound of Formula II. The values of m, p and q and the definitions of R1 and R2 can vary from monomer to monomer for any given value of xe2x80x9cnxe2x80x9d monomers.
In yet another aspect, this invention relates to a compound of Formula III: 
In Formula III, R is a functional group including, but not limited to, hydrogen, alkyl or aryl. R1 and R2 are functional groups which may be the same or different and include, but are not limited to, hydrogen or alkyl. In another embodiment, R, R1 and the nitrogen to which they are bound form an azido moiety. R6 and R7 are functional groups which may be the same or different and include, but are not limited to, hydrogen, optionally substituted alkyl or optionally substituted aryl, wherein the substituents include aryl, amino, carboxyl, thiol or hydroxy groups or the side chain of any natural or synthetic amino acid or amino acid mimetic. The index xe2x80x9cvxe2x80x9d is an integer having a value ranging from 2 to 40; the indexes xe2x80x9cmxe2x80x9d and xe2x80x9crxe2x80x9d are independently selected and have values ranging from 2 to 6; the indexes xe2x80x9cxxe2x80x9d and xe2x80x9csxe2x80x9d are independently selected and have values ranging from 1 to 4; z and t are independently 0 or 1; and R3, in Formula III, is a functional group including, but not limited to, halogen, hydrogen, alkoxy, mercapto, hydrazino, amino or NR4R5, wherein R4 and R5 are independently hydrogen or alkyl. The parenthesis between R and R3 define a monomeric unit. R1, m, R6, z, x, r, R7 and t can be the same or different throughout the series of xe2x80x9cvxe2x80x9d monomers.
In still yet another aspect, this invention relates to a compound of Formula IV: 
In Formula IV, R1 and R2 are functional groups which may be the same or different and include, but are not limited to, hydrogen or alkyl. R6 and R7 in Formula IV, are functional groups which may be the same or different and include, but are not limited to, hydrogen, optionally substituted alkyl or optionally substituted aryl, wherein the substituents include aryl, amino, carboxyl, thiol or hydroxy groups or the side chain of any natural or synthetic amino acid or amino acid mimetic. The index xe2x80x9cvxe2x80x9d is an integer having a value ranging from 2 to 40; the indexes xe2x80x9cmxe2x80x9d and xe2x80x9crxe2x80x9d are independently selected and have values ranging from 2 to 6; the indexes xe2x80x9cxxe2x80x9d and xe2x80x9csxe2x80x9d are independently selected and have values ranging from 1 to 4; z and t are independently 0 or 1. A, in Formula IV, is a functional group including, but not limited to, hydrogen, alkyl, acyl or a ligand. In an alternative embodiment, R1, A, and the nitrogen to which they are bound form an azido moiety. B, in Formula IV, is a functional group including, but not limited to, halogen, hydroxy, alkoxy, amino, NR4R5 (wherein R4 and R5 are independently hydrogen or alkyl), mercapto, hydrazino, diacylglycerolyl, dialkylglycerolyl, N,N-dialkylamino, 1,2-diacyloxy-3-aminopropane, 1,2-dialkyloxy-3-aminopropane and a ligand. The parenthesis between A and B define a monomeric unit. R1, m, R6, z, x, r, R7 and t can be the same or different throughout the series of xe2x80x9cvxe2x80x9d monomers.
In certain aspects, the present invention relates to intrinsically heterobifunctional polyamide oligomers that serve, inter alia, as a replacement to PEG, because they have superior properties. In these aspects, the oligomeric structures defined herein provide the following surprising advantages over PEG. First, unlike PEG which exists as a distribution of molecular weights, the oligomers of the present invention are of known molecular weights. Second, the present invention relates to biodegradable oligomeric material. Third, the present oligomers are intrinsically heterobifunctional bridges that can be used without the need to activate the end groups as in PEG polymers. Fourth, the present oligomers are hydrophilic, thereby providing a convenient way to keep other material in solution. There are other advantages of this invention which will be apparent to those skilled in the art.
In yet another aspect, this invention relates to a liposome, a micelle, a virosome, a lipid-nucleic acid particle, or other drug delivery composition containing a lipid conjugated to the polyamide oligomer of Formula II or Formula IV.
In yet another aspect, a liposome, a micelle, a virosome, a lipid-nucleic acid particle, or other drug delivery composition contains surface-bound ligand molecules, targeting vectors, antibodies or reporter molecules to bind to specific target tissues or cells.
In another aspect, the compound of Formula II or Formula IV is a bridge, i.e., a linker molecule, with at least one ligand molecule (e.g., an antibody) covalently attached thereto. In a presently preferred embodiment, the compound of Formula II or Formula IV is a bridge with at least two ligand molecules (e.g., an antibody and a therapeutic peptide) covalently attached thereto.
In still yet another aspect, this invention relates to a liposome, a micelle, a virosome, a lipid-nucleic acid particle, or other drug delivery composition for administering a bioactive agent via the bloodstream.
In another aspect, this invention relates to a method of enhancing the blood-circulation time of liposomes, micelles, virosomes, lipid-nucleic acid particles or other lipidized drug delivery compositions administered intravenously. The enhanced circulation time is achieved by adding to the liposomes, micelles, virosomes, lipid-nucleic acid particles or other drug delivery compositions an amphipathic lipid derivatized with a compound of Formula II or Formula IV.
Other features, objects and advantages of the invention and its preferred embodiments will become apparent from the detailed description which follows.